Unable to use available minutes to phone landline numbers

Telkom Mobile "upgraded" me from the "SmartPlan 50 Deal" to the "FreeMe 500MB Deal" in January 2018. On the "new" deal I am supposed to get "300 free minutes per month to phone Telkom Mobile and Telkom Fixed lines", but 90% of the time when I phone landline numbers I get a voice telling me that I have "insufficient funds" available, yet my balance is 2857 minutes available.